function Line () {
  this.x = 0
  this.y = 0
  this.color = '#ffff00'
  this.lineColor = "#000000"
  this.rotation = -Math.PI/2
  this.width = 0
  this.height = 0
  this.radius = 120
  this.composite = 'source-over'
}

Line.prototype.draw = function (ctx) {
  ctx.imageSmoothingQuality = 'high'
  // ctx.clearRect(this.x, this.y, this.width, this.height)
  ctx.save()
  ctx.translate(this.x, this.y, this.width, this.height)
  ctx.rotate(this.rotation)
  ctx.globalCompositeOperation = this.composite
  ctx.lineWidth = 2
  ctx.strokeStyle = this.lineColor
  ctx.beginPath()
  ctx.moveTo(this.radius, 0) // 左边底角（开始）
  ctx.lineTo(this.radius + 3,0) // 左边内角
  ctx.stroke()
  ctx.restore()
}
